Systems for inspection of shrouds

ABSTRACT

A system to measure thickness of a shroud is provided. The system includes at least one resistive element embedded within the shroud. A reduction in a cross-sectional area of the at least one resistive due to wearing out of the shroud results in a change in a resistance of the at least one resistive. The system also includes an impedance measurement device that measures a total resistance associated with the at least one resistive element.

BACKGROUND

The invention relates generally to systems and methods for assessingwear or damage to turbine parts and more specifically, to wear in ashroud of the turbine.

There are several techniques that are currently used for inspection ofturbine parts. A commonly used technique includes schedule-basedshutting down of a turbine and physically examining parts atpredetermined intervals. However, the process is inefficient, timeconsuming, and costly due to turbine shut down and maintenance. Further,several on-line methods have been developed for detecting wear-out ofturbine parts such as, but not limited to, shrouds.

For example, Blatchley and coworkers (C. C. Blatchley and R. J. BricaultJr., in Tribological Mechanisms & Wear Problems in Materials, ASMInternational, Metals Park, Ohio, 1987, pp. 95-100 and C. C. Blatchleyand P. G. Loges, in Advances in Steam Turbine Technology for PowerGeneration, ASME, New York, N.Y., 1990, Vol. 10, pp. 9-13) developed a“surface layer activation” technique to monitor wear and corrosion insteam turbines by detecting gamma-ray signals from radionuclidesimbedded in trace amounts in surfaces of wearing parts. The nuclidesserved as surface markers, and were produced by controlled exposure toparticles from Van de Graaff or cyclotron accelerators.

However, the above techniques can only be applied to steam turbines,which are closed systems, so that radioactive materials in the waterstream will not be released to the environment. The technique cannot beapplied to gas turbines because the exhaust is released into the air,and radioactive elements will be detrimental to the environment. Also, agas sampling and analysis system would be needed in the area of theexhaust stream if one decided to use this technique on gas turbineengines. This technique further finds challenges in aircraft enginesystems where the sampling and analysis system needs to occur online orduring flight, thus increasing the complexity.

There are other existing coating life estimation methods that aretypically based on average effects of stress and temperature profiles ofthe parts. Such methods are unable to focus on individual parts sincethey do not take into account conditions that the parts installed in aparticular turbine actually encounter, such as, but not limited to,foreign object damage, variation of operating conditions from site tosite, and occasional overfiring of the turbine. All of the conditionscan drastically influence the true remaining life of the individualparts. Blade rubs also contribute to conditions where a small portion ofthe shroud may experience more localized damage than the rest of theshroud.

Thus, there exists a need for an on-line assessment of wear of gasturbine parts that addresses one or more aforementioned issues. Inapplications that utilize a clearance control system, since clearancemeasurements typically measure the distance between the installed sensorand the blades and assesses the blade to shroud clearance based on theexpected shroud thickness, accurate assessment of the extent of shroudwear is necessary to maintain the clearance measurement accuracy of thesystem.

BRIEF DESCRIPTION

In accordance with an embodiment of the invention, a system to measurethickness of a shroud is provided. The system includes at least oneresistive element embedded within the shroud. The system also includesan impedance measurement device configured to measure a total resistanceassociated with the at least one resistive element.

In accordance with another embodiment of the invention, a system formeasuring thickness of a shroud is provided. The system includes anelectronic circuit embedded within the shroud. The electronic circuitincludes an inductor and a capacitor coupled to the inductor, such thata capacitance of the capacitor is a function of a wear of the shroud.

In accordance with another embodiment of the invention, a system formeasuring thickness of a shroud is provided. The system includes anelectronic circuit embedded within the thermal barrier coating and theabradable coating layer. The electronic circuit includes an inductor anda capacitor coupled to the inductor. The thermal barrier coating and theabradable coating serve as a magnetic material forming the core of theinductor, such that a inductance of the inductor is a function of a wearof the shroud.

In accordance with another embodiment of the invention, a system formeasuring thickness of a shroud is provided. The system includes a bulkelectrode embedded within the shroud, wherein a reduction in across-sectional area of the electrode due to wearing out of the shroudresults in a change in a resistance of the electrode. The system alsoincludes an impedance measurement device configured to measure theresistance of the bulk electrode.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic illustration of a typical turbine blade systemincluding multiple blades and a shroud;

FIG. 2 is a schematic cross-sectional view of a system for measuringthickness of the shroud in FIG. 1, in accordance with embodiments of theinvention.

FIG. 3 is a schematic illustration of an exemplary measurement systemincluding multiple wires embedded at different radial depths at a givenposition on a circumference of the shroud in FIG. 1, in accordance withembodiments of the invention.

FIG. 4 is a schematic representation of another exemplary systemincluding a LC circuit, to measure thickness of a shroud in accordancewith embodiments of the invention.

FIG. 5 is a schematic of a cross-sectional view of an exemplaryimplementation of the system in FIG. 4.

FIG. 6 is a schematic illustration of another exemplary system includinga bulk electrode, to measure thickness of a shroud in accordance withembodiments of the invention;

FIG. 7 is a schematic illustration of another exemplary system includinga bulk electrode and a reference electrode, to measure thickness of ashroud in accordance with embodiments of the invention;

FIG. 8 is a flow chart representing steps in an exemplary method formeasuring thickness of a shroud; and

FIG. 9 is a flow chart representing steps in another exemplary methodfor measuring thickness of a shroud.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the invention includesystems and methods for inspection of a shroud. Embodiments of theinvention disclosed herein, assess wear on the shroud by measuringthickness of the shroud. More specifically, a change in resistance ofone or more resistive elements embedded within the shroud is measured,which occurs due to wearing out of the shrouds. The wearing of theshroud may occur due to various reasons. A non-limiting example includeswearing away of the shroud due to rubs that occur between a tip of aturbine blade and the shroud.

FIG. 1 is a schematic illustration of a typical turbine blade system 10including multiple blades 12 and a shroud 14 separated by a clearance16. A reduction of the clearance 16 may result in rubbing of a tip 17 ofthe blades 12 against the shroud 14. Such an interaction may betolerated by providing an abradable coating layer 18 deposited upon athermal barrier coating layer 20. The abradable coating layer 18 isdesigned to release fine wear debris when machined by the blades 12rotating at a high velocity, while causing minimal wear of the blades12.

FIG. 2 is a schematic cross-sectional view of a system 30 for measuringthickness of the shroud 14 in FIG. 1. In the illustrated embodiment, acombination of a thermal barrier coating layer and an abradable coatinglayer 32 is deposited on a base portion of the shroud 14. In aparticular embodiment, the thermal bather coating layer 32 has athickness of about 0.005 inch to about 0.1 inch. In an exemplaryembodiment, the abradable coating layer has a thickness of about 0.005inch to about 0.1 inch. The system 30 includes at least one resistiveelement 38 that is embedded within the barrier and abradable coatinglayers 32. It should be noted that in absence of the thermal barriercoating layer and the abradable coating layer, the resistive element 38is embedded within the shroud. In a particular embodiment, the at leastone resistive element 38 is embedded within the thermal barrier coatingand the abradable coating layers via a deposition process such as, butnot limited to, a direct write printing process, an ink jet process or adecal process. In a particular embodiment, each of the at least oneresistive element 18 comprises a single material. In another embodiment,the resistive element comprises multiple geometries resulting indifferent resistivities. In yet another embodiment, each of the at leastone resistive element 38 comprises multiple materials having differentresistivities. Non-limiting examples of the materials used are platinum,platinum-rhodium, platinum-iridium, nickel, or tungsten with appropriateoxidization protection. In yet another embodiment, the resistive element38 is deposited directly into a shroud material. An impedancemeasurement device 40 measures a total resistance associated with the atleast one resistive element 38. In one embodiment, the impedance ismeasured by applying a known current, and measuring the voltage dropacross the resistive element 38. In another embodiment, a known voltageis applied, and the associated current is measured to determine theresistance of the resistive element 38. A processor 37 is optionallycoupled to the impedance measurement device 40 and is configured toconvert the resistance to a shroud thickness value.

For the example embodiment illustrated by FIGS. 2 and 4, the at leastone resistive element 38 includes multiple wires R1, R2 . . . R5. Forthis configuration, a break in at least one of the wires due to a wearin the shroud corresponds to a change in a total resistance of thewires, such that the impedance measurement device measures a stepwiseincrease in resistance due to the wear on the shroud. It should be notedthat the 5 wires shown in FIG. 2 are merely illustrative and othernumbers of wires can be employed. According to a particular embodiment,at least a subset of the wires are equipped with at least two contactpoints to measure the resistance, such that the total resistancecomprises an equivalent resistance in a parallel connection of thewires.

For the example arrangement depicted in FIG. 3, multiple resistiveelements 38 are embedded at different locations around a circumferenceof the shroud. In a non-limiting example, the different locations arespaced at about 10 degrees apart circumferentially. For the exemplaryarrangement shown in FIG. 3, the resistive elements 38 are multiplewires that are embedded at different radial depths, such that at least asubset of the wires are arranged at different radial positions at agiven position along the circumference of the shroud. In one embodiment,the resistance of the wires embedded at different depths is the same. Inanother embodiment, the resistance of the wires at the different depthsare different. This enables calibration of the measurements relative totemperature. In one embodiment, each of the wires has a diameter in arange between about 1 mil to about 20 mil. depending on the process usedto deposit the wires.

In another exemplary embodiment, each of the at least one resistiveelement 38 comprises a bulk resistive element, wherein a wear in theshroud corresponds to a change in a resistance of the bulk resistiveelement. For certain embodiments, the bulk resistive element(s)comprises a single material. For other embodiments, the bulk resistiveelement(s) comprises multiple materials with different resistivities.

FIG. 3 is a schematic illustration of an exemplary measurement system42. The system 42 includes multiple wires 44 embedded at differentradial depths 46 at a given position 48 on a circumference of the shroud14. In the illustrated example, the system 42 includes five wires. Asnoted above, the example arrangement of five wires is illustrative andis non-limiting. An impedance measurement device 49 measures a totalresistance associated with the wires 44. In a particular embodiment, theresistance of the wires 44 embedded at the different depths 46 is thesame. In another embodiment, the resistance of the wires 44 embedded atdifferent depths 46 is different. This latter arrangement can beaccomplished, for example, by using wires formed of different materialsand/or using wires having different geometries and/or dimensions.

FIG. 4 is a schematic illustration of another exemplary system 60 tomeasure thickness of a shroud 14, as referenced in FIG. 1. The system 60includes an electronic circuit 62 embedded within a thermal barriercoating layer and an abradable coating layer (not shown). It should benoted that in absence of the thermal barrier coating layer and theabradable coating layer, the electronic circuit 62 is embedded withinthe shroud 14. The electronic circuit 62 includes an inductor 64 that iscoupled to a capacitor 66. The capacitor 66 is formed such that thethermal barrier coating and the abradable coating layer serve as adielectric material of the capacitor, wherein a capacitance of thecapacitor 66 is a function of a wear of the shroud. In a case wherethere is no thermal barrier coating, the abradable coating and/or theshroud material will serve as a dielectric material of the capacitor. Inanother embodiment, an explicit high temperature dielectric materialsuch as, for example, alumina can be used as the dielectric material ofthe capacitor 66. For the example arrangement depicted in FIG. 5, thecapacitor 66 comprises a capacitive comb deposited between the thermalbarrier coating layer and the abradable layer. For the arrangement shownin FIG. 4, a remote reader 68 measures a resonance frequency of theelectronic circuit 62. In a particular embodiment, the remote readercomprises a coil deposited outside of the shroud. The system 60optionally includes a processor 69 that is configured to receive thedata from the remote reader 68 and to convert the data to a shroudthickness value. In another exemplary embodiment, the thermal barriercoating and the abradable coating serve as a magnetic material formingthe core of the inductor 64, such that an inductance of the inductor 64is a function of a wear of the shroud.

FIG. 5 is a schematic of a top view of a physical structure of thesystem 60 in FIG. 4. In the illustrated embodiment, the capacitor 66 isa comb structure with a thermal barrier coating layer and abradablecoating layer 64 forming a dielectric between wires 70. It should benoted that in absence of the thermal barrier coating layer and theabradable coating layer, the electronic circuit 62 is embedded withinthe shroud 14. In another nonlimiting example, the capacitor 66comprises a parallel plate capacitor with the TBC and abradable layersserving as the dielectric material. In all of these examples, a wear inthe shroud 14 leads to wearing out of the dielectric, consequentlyresulting in a change in capacitance. The remote reader 68 measures atransient frequency that is a function of the capacitance.

FIG. 6 is a schematic illustration of another exemplary system 90 tomeasure thickness of a shroud. The system 90 includes a bulk electrode92 of length referenced by numeral 93 embedded within a thermal barriercoating layer and an abradable coating layer 94, or directly in a shroudmaterial wherein a reduction in a cross-sectional area of the electrode92 due to wearing out of the shroud results in a change in a resistanceof the electrode 92. It should be noted that in absence of the thermalbarrier coating layer and the abradable coating layer, the bulkelectrode 92 is embedded within the shroud 14. Non-limiting examples ofa material used in the electrode include platinum, platinum-rhodium,platinum-iridium, nickel, or tungsten with appropriate oxidizationprotection. An impedance measurement device 96 measures resistance ofthe bulk electrode 92. A processor 97 is optionally coupled to theimpedance measurement device 96 and is configured to receive data fromthe electrode(s). In one embodiment, the impedance is measured byapplying a known current, and measuring the voltage drop across the bulkelectrode 92. In another embodiment, a known voltage is applied, and theassociated current is measured to determine the resistance of the bulkelectrode 92.

FIG. 7 is a schematic illustration of yet another exemplary measurementsystem 100, which is similar to the system 90 discussed above withreference to FIG. 6 but further includes a reference electrode 102. Thereference electrode 102 is deposited at a depth in the shroud 14 suchthat a resistance of the reference electrode changes only as a result ofa change in environmental factors such as, but not limited to,temperature and pressure. Namely, the reference electrode is depositedwell below the surface of the abradable and TBC coatings, (or bareshroud surface if a TBC coat is not deposited on the shroud) such thatthe reference electrode is not subject to wear during rotation ofturbine blades. Accordingly, the reference electrode 102 enablescalibration of the impedance measurement of the electrode 92 in FIG. 5.As indicated, an impedance measurement device 96 compares a change inresistance in electrode 92 that is affected by a wear in the shroud 14in addition to the change in environmental conditions, with a change inresistance of the reference electrode 102, which is only affected by thechange in environmental conditions.

FIG. 8 is a flow chart representing steps in an exemplary method 120 formeasuring thickness of a shroud. The method 120 includes positioning atleast one resistive element adjacent to a surface of a shroud in step122. A thermal barrier coating is deposited in step 124 on the surfaceof the shroud to partially embed the at least one resistive element. Anabradable coating is further deposited on the thermal barrier coating instep 126 to fully embed the at least one resistive element. If a TBCcoating is not used, the element can be built directly into a shroudmaterial. A total resistance associated with the at least one resistiveelement is measured in step 128 to detect a wear on the shroud.

FIG. 9 is a flow chart representing another exemplary method 140 formeasuring thickness of a shroud. The method 140 includes depositing athermal barrier coating on a surface of the shroud in step 142. At leastone resistive element is partially deposited during the deposition ofthe thermal barrier coating in step 144. An abradable coating isdeposited on the thermal barrier coating in step 146 and deposition ofthe at least one resistive element is simultaneously completed such thatthe at least one resistive element is embedded in the thermal barriercoating and the abradable coating. In a particular embodiment, theresistive element (s) is/are deposited via a direct write process. Inanother embodiment, the resistive element (s) is/are deposited via anink-jet process. In yet another embodiment, the resistive element (s)is/are deposited via a decal process. In another embodiment, theresistive element(s) are built directly into the shroud material withseveral of the manufacturing methods available. A total resistanceassociated with the at least one resistive element is measured in step148 to detect a wear on the shroud.

The various embodiments of systems and methods for inspection of shroudsdescribed above thus provide an online assessment of wear—in a shroud ina turbine engine. Additionally, the techniques and systems may be usedin engines outfitted with a clearance sensor and/or having an activeclearance control system. In addition, the present techniques enableaccurate blade to shroud clearance measurement in presence of a shroudwear. Further, the techniques enable localization of rubs in the shroudoccurring due to the blades, thus reducing clearance added to compensatefor out of roundness. These techniques and systems also allow forimproved turbine prognosis and field inspection techniques.

Of course, it is to be understood that not necessarily all such objectsor advantages described above may be achieved in accordance with anyparticular embodiment. Thus, for example, those skilled in the art willrecognize that the systems and techniques described herein may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

Furthermore, the skilled artisan will recognize the interchangeabilityof various features from different embodiments. For example, the use ofan example of multiple bulk resistive elements described with respect toone embodiment can be adapted for use in a system employing resistiveelements at various radial depths with different resistances describedwith respect to another. Similarly, the various features described, aswell as other known equivalents for each feature, can be mixed andmatched by one of ordinary skill in this art to construct additionalsystems and techniques in accordance with principles of this disclosure.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A system for measuring thickness of ashroud, the system comprising: a bulk electrode embedded within theshroud, wherein a reduction in a cross-sectional area of the bulkelectrode due to wearing out of the shroud results in a change in aresistance of the bulk electrode; and an impedance measurement deviceconfigured to measure the resistance of the bulk electrode, wherein theresistance of the bulk electrode is measured by one of applying a knowncurrent, and measuring a voltage drop across the bulk electrode or byapplying a known voltage, and measuring a current across the bulkelectrode.
 2. The system of claim 1, further comprising a referenceelectrode embedded within the shroud, wherein a resistance of thereference electrode is configured to change only as a result of changein environmental factors.
 3. The system of claim 2, wherein the shroudcomprises a thermal barrier coating deposited on a base portion of theshroud and an abradable coating layer deposited on the thermal barriercoating, and wherein the reference electrode is deposited below thethermal barrier coating layer such that the reference electrode is notsubject to wear.
 4. The system of claim 2, wherein the environmentalfactors include at least one of temperature or pressure.
 5. The systemof claim 2, wherein the reference electrode enables calibration of theimpedance measurement of the bulk electrode.
 6. The system of claim 1,wherein the shroud comprises a thermal barrier coating deposited on abase portion of the shroud and an abradable coating layer deposited onthe thermal barrier coating, and wherein the bulk electrode is embeddedwithin at least one of the thermal barrier coating and the abradablecoating.
 7. The system of claim 6, wherein the bulk electrode isembedded in the thermal barrier coating and the abradables coating. 8.The system of claim 1, wherein the bulk electrode is comprised of atleast one of platinum, platinum-rhodium, platinum-iridium, nickel, ortungsten.
 9. The system of claim 1, further comprising a processorcoupled to the impedance measurement device and configured to receivedata from the bulk electrode.
 10. A system for measuring thickness of ashroud, the system comprising: a bulk electrode embedded within theshroud, wherein a reduction in a cross- sectional area of the bulkelectrode due to wearing out of the shroud results in a change in aresistance of the bulk electrode; an impedance measurement deviceconfigured to measure the resistance of the bulk electrode; and areference electrode embedded within the shroud, wherein a resistance ofthe reference electrode is configured to change only as a result ofchange in environmental factors, wherein the shroud comprises a thermalbarrier coating deposited on a base portion of the shroud and anabradable coating layer deposited on the thermal barrier coating, andwherein the bulk electrode is embedded within at least one of thethermal barrier coating and the abradable coating and wherein thereference electrode is deposited below the thermal barrier coating layersuch that the reference electrode is not subject to wear.
 11. The systemof claim 10, further comprising a processor coupled to the impedancemeasurement device and configured to receive data from the bulkelectrode.
 12. The system of claim 10, wherein the resistance of thebulk electrode is measured by applying a known current, and measuringthe voltage drop across the bulk electrode.
 13. The system of claim 10,wherein the resistance of the bulk electrode is measured by applying aknown voltage, and measuring the current across the bulk electrode.